How to write data to mutiple QFiles - qt

Question

I am trying to add a line to the file every time i receive data, and if the number of lines exceed 10 lines, create new files to store the data until create 5 files, but i encoutered a problem, that is the application will crash at the 56th line : QTextStream stream(current_record_file); , the code are :
mainwindow.cpp:
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
simulateReceiveData();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::simulateReceiveData()
{
while(file_count < 5){
qDebug()<<"on recording ...";
if(file_count == 1 && msg_line_count == -1){
//create the very first new file
record_file_name_prefix = "D:/Project/MessageRecording";
QString record_file_name = record_file_name_prefix + "(1).asc";
qDebug()<<"record_file_name is"<<record_file_name;
QFile file(record_file_name);
if (!file.open(QFile::WriteOnly | QFile::Truncate)){
qDebug()<<QString("Fail to open file : %1").arg(record_file_name);
return;
}
//write the header
current_record_file = &file;
QTextStream stream(current_record_file);
stream << "START\r\n";
msg_line_count = 0;
}else if(msg_line_count == 10){
//write footer to privious file
QTextStream stream(current_record_file);
stream << "END";
stream.flush();
current_record_file->close();
//create next new file
file_count++;
QString record_file_name = record_file_name_prefix + QString("(%1).%2").arg(file_count).arg("asc");
QFile file(record_file_name);
if (!file.open(QFile::WriteOnly | QFile::Truncate))
return;
current_record_file = &file; //redirect to the new created file
msg_line_count = 0;
}else{
//write the main body
QTextStream stream(current_record_file); // CRASH HERE !
stream <<"0.0000 0 Rx 00 00 00 00 00 00 00 00\r\n";
msg_line_count++;
}
}
}
mainwindow.h :
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QFile>
#include <QDateTime>
#include <QTextStream>
#include <QDebug>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
private:
Ui::MainWindow *ui;
void simulateReceiveData();
int file_count = 1;//number of files
int msg_line_count = -1;//number of lines in one file
QString record_file_name_prefix;
QFile* current_record_file = nullptr;//point to currently written file
};
#endif // MAINWINDOW_H

Answer 1

As stated by chehrlic's comment, you are accessing a (dangling) pointer to an object that has gone out-of-scope.
Two solutions exist:
Reopen the file on each write (may be incompatible with QFile::Truncate and less efficient)
Use QFile current_record_file as a member, instead of QFile* current_record_file. This seems to me the best approach.

Answer 2

Thanks for everyone's reply, i tried m7913d's second solution, and it can create multiple QFiles now ! The magic point is after you close last QFile current_record_file, and reset its file name by current_record_file.setFileName(record_file_name);, programm will help us create new file automatically. The new worrkable code are :
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
simulateReceiveData();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::simulateReceiveData()
{
while(file_count < 5){
qDebug()<<"on recording ...";
if(file_count == 1 && msg_line_count == -1){
//create the very first new file
record_file_name_prefix = "D:/Project/MessageRecording";
QString record_file_name = record_file_name_prefix + QString::number(file_count) + ".asc";
current_record_file.setFileName(record_file_name);
if (!current_record_file.open(QFile::WriteOnly | QFile::Truncate)){
qDebug()<<QString("Fail to open file : %1").arg(record_file_name);
return;
}
//write the header
QTextStream stream(&current_record_file);
stream << "START\r\n";
msg_line_count = 0;
}else if(msg_line_count == 10){
//write footer to privious file
QTextStream stream(&current_record_file);
stream << "END";
stream.flush();
current_record_file.close();
file_count++;
QString record_file_name = record_file_name_prefix + QString::number(file_count) + ".asc";
qDebug()<<"new record file is"<<record_file_name;
current_record_file.setFileName(record_file_name);
if (!current_record_file.open(QFile::WriteOnly | QFile::Truncate)){
qDebug()<<QString("Fail to open file : %1").arg(record_file_name);
return;
}
QTextStream stream2(&current_record_file);
stream2 << "START\r\n";
msg_line_count = 0;
}else{
//write the main body
QTextStream stream(&current_record_file); // CRASH HERE !
stream <<file_count<<" 0.0000 0 Rx 00 00 00 00 00 00 00 00\r\n";
msg_line_count++;
QThread::sleep(1);
}
}
}
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QFile>
#include <QDateTime>
#include <QTextStream>
#include <QDebug>
QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();
private:
Ui::MainWindow *ui;
void simulateReceiveData();
int file_count = 1;//number of files
int msg_line_count = -1;//number of lines in one file
QString record_file_name_prefix;
QFile current_record_file;
};
#endif // MAINWINDOW_H